The 3rd Generation Partnership Project Evolved Universal Terrestrial Radio Access (E-UTRA) Long Term Evolution (LTE) Rel. 8 to 10 control signals include Physical Control Format Indicator CHannel (PCFICH), Physical Hybrid ARQ Indicator CHannel (PHICH) and Physical Downlink Control CHannel (PDCCH).
Legacy PDCCH in LTE Rel. 8 to 10 is designed with Cell specific Reference Symbols (CRS) based transmission. A PDCCH is scrambled with the Cell Radio Network Temporary Identifier (C-RNTI) of the user being scheduled and precoded with 1/2/4 transmit diversity, cross-interleaved with other PDCCHs and then transmitted in the entire system bandwidth in the control region of a subframe. The control region contains the first N Orthogonal Frequency Division Multiplexing (OFDM) symbols in the first slot of a subframe. The value of N is N=1, 2, 3 or 4 in case of 1.4 MHz bandwidth and is signalled in the PCFICH. Through CRS-based transmit diversity and cross-interleaving within the system bandwidth, Rel. 10 PDCCH exploits spatial and frequency diversity to maximize the robustness of the control signal and ensures its reliable reception and coverage in a cell. A PDCCH may carry a DL grant or an UL grant.
LTE Rel. 10 introduces a new PDCCH transmission scheme for macro-relay backhaul link called R-PDCCH. R-PDCCH inherits all the Downlink Control Information (DCI) formats of legacy LTE system including DCI 1, 1A, 1B, 1C, 2, 2A, 2B, 2C and 4 but relies on Demodulation Reference Signal (DMRS) based transmission instead of CRS based transmit diversity. Thus for each relay node, a semi-statically configured downlink resource is reserved for the eNB-to-RN link by higher-layer. This resource is used for R-PDCCH and R-PDSCH transmission. In the frequency domain the reserved resource features a set of NR-PDCCH resource blocks. In the time domain the transmission resource features a group of OFDM symbols in the respective first slot and second slot. The first slot is used for DL grant transmission. The second slot is used for UL grant transmission. The reserved resources of both the first and second slots can be also used for R-PDSCH in the eNB-to-RN backhaul link, provided that they are not occupied by R-PDCCH.
When a relay is configured with R-PDCCH with cross-interleaving: R-PDCCH is transmitted with CRS-based transmit diversity according to the same procedure as in legacy LTE system, except that interleaving is done in the virtual system bandwidth of NR-PDCCH Resource Blocks (RBs).
When a relay is configured with R-PDCCH without cross-interleaving: R-PDCCH can be transmitted with CRS-based transmit diversity in the NR-PDCCH RBs. Alternatively, R-PDCCH can be transmitted with DMRS-based rank-1 precoding in the NR-PDCCH RBs, on antenna port 7 with a scrambling sequence ID (SCID) of 0. The actual number of Physical Resource Blocks (PRBs) used for R-PDCCH depends on the R-PDCCH aggregation level and candidate index.